The present invention relates to the field of minimally invasive, percutaneous procedures such as angioplasty. In particular, the invention relates to a distal filter for use during such a procedure.
Angioplasty, atherectomy and stent placement, among other procedures, have become well accepted for treatment of coronary lesions. These procedures are often performed as an alternative to coronary bypass. It is also possible, however, that a saphenous vein graft, which is used to bypass coronary lesions, may itself develop a lesion. These lesions may also be treated by minimally invasive procedures such as angioplasty, atherectomy and/or stent placement.
When lesions are treated by these minimally invasive, percutaneous methods, it is possible that particles of plaque, thrombus or other material may break loose from the lesion and drift distally into the smaller coronary arteries. When these minimally invasive methods are performed on native arteries, the plaque or thrombus released during the procedure rarely cause embolization. When these procedures are performed on saphenous vein grafts, however, the incidence of embolism due to the breaking off of plaque or thrombus from the vein graft is substantially greater than from native arteries.
The increased incidence of embolization is believed to be due, at least in part, to the larger diameter of the bypass graft relative to the native artery. The larger diameter of the graft results in a slower blood flow velocity through the graft than the native artery. In addition, the plaque and thrombus of vein grafts is somewhat more fragile than that found in native arteries.
As the difference in embolism associated with treatment of native arteries and vein grafts has been noted, it would be desirable to develop techniques to reduce embolism associated with treatment of vein graft lesions. Additionally, where stent rid placement or other minimally invasive treatments are performed on the carotid artery, it would be desirable to limit the drift of plaque and thrombus toward the brain.
The present invention pertains to an intravascular filter for use during minimally invasive percutaneous procedures. The filter is preferably placed distally, within the blood stream, of the site of the interventional procedure. The filter may be used to filter plaque, thrombus and other debris released into the blood stream during minimally invasive procedures performed in blood vessels.
A filter assembly in accordance with the present invention includes a catheter including an elongate shaft having a proximal end and a distal end. A housing is disposed at the distal end of the shaft. The housing itself has a distal end. An elongate wire extends at least in part through the catheter. The wire has a proximal end and a distal end. A filter is connected to the wire proximate the distal end of the wire. The filter, during delivery and retrieval from its deployment site is preferably at least, in part, disposed within the housing.
By retracting the catheter relative to the filter, the filter emerges from within the housing to a position outside the housing for deployment of the filter. When the filter is disposed outside the housing, the filter can be drawn into the housing by pushing the housing over the filter. It is preferable, however, to retrieve the filter with a different catheter having a housing having a larger inside diameter than the housing of the catheter used to deliver the filter.
It is preferable that the distal end of the housing be atraumatic. This can be accomplished by using a soft atraumatic material for the filter distal end. Additionally, if the catheter is a delivery catheter, the distal end can also be tapered by heat shrinking the distal end of the housing around a portion of the filter. The filter itself can also be slightly wider than the distal end of the housing such that the filter acts as an atraumatic distal end of the filter assembly. The distal end of the housing can also be rounded inwardly toward the filter. In yet another embodiment, the distal end of the housing can include an elastomeric sheath which tapers distally. In still another embodiment of the filter assembly, a collapsible shell can be connected to the wire. The shell is preferably disposed substantially distally of the filter. The wire can include a spring tip.
Where the catheter is a retrieval catheter, a housing atraumatic tip insert can be disposed within the housing and extend distally therefrom while the filter is positioned outside the housing. The insert preferably tapers distally. In one embodiment, the insert can be releasably connected to the distal end of the housing. In a preferred embodiment, the insert includes a balloon. In yet another embodiment, the insert includes a flap which extends transversely over the distal end of the housing. When the filter is withdrawn into the housing, the insert is drawn proximally into the housing as well.
The elongate shaft of the filter assembly can have an elongate wire lumen running through its length. In such a configuration, the catheter can be considered an over-the-wire catheter. The catheter can be converted to a single operator exchange catheter by dividing the shaft into two or more elongate segments and coupling the segments together. The length of the segments should be such that they can be uncoupled or coupled as they are being withdrawn or advanced over the wire. The coupling could include a bayonet fastener or a threaded fastener for example. As an alternative to the coupling, the catheter can be configured for a single operator exchange by providing a telescoping or collapsible portion. The collapsible portion can include a member which can have a braided portion. In an alternate embodiment, the catheter can include longitudinal slits for removal of the catheter from the wire.
The filter itself is disposed at the distal end of the wire. The filter includes an expandable frame and filter membrane. The frame can include a nickel titanium alloy. The membrane preferably surrounds a portion of the wire and is configured to taper distally. The membrane preferably includes polyurethane and defines a plurality of apertures. Once the filter is deployed distally of the lesion to be treated, the wire can be used as a guidewire for advancing angioplasty, atherectomy, or other devices thereover.